FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a ferrule according to the preamble of claim 1 , which is configured for detachable mounting to a lower end portion of a crutch, cane, walking stick or ski stick.

The ferrule according to the present invention is particularly intended to be mounted to a walking aid in the form of a crutch, cane or walking stick. However, the ferrule may also be mounted to a ski stick for use in roller skiing.

Ferrules for detachable mounting to a lower end portion of a crutch, cane or walking stick are known in various configurations. Such ferrules are for instance disclosed in GB 2545253 A, US 994194 A, US 2014/01 16483 A1 and US 2014/0209135 A1. A ferrule of this type may have a ground-engaging member of resiliently deformable high-friction material, such as rubber or rubber-like plastic material, in order to provide enhanced grip on slippery surfaces and thereby prevent the crutch, cane or walking stick from slipping on the surface on which it bears and in order to absorb impacts and thereby offer improved comfort to the person using the crutch, cane or walking stick.

SUMMARY OF THE INVENTION

The object of the present invention is to achieve a further development of a ferrule of the above-mentioned type so as to provide a ferrule that is improved in at least some aspect.

According to the invention, this object is achieved by means of a ferrule having the features defined in claim 1.

The ferrule of the present invention comprises an upper ferrule part with a socket for detachable engagement with a lower end portion of a crutch, cane, walking stick or ski stick, and a ground- engaging lower ferrule part releasably mountable to the upper ferrule part. The lower ferrule part is releasably mountable to the upper ferrule part through a snap-fit coupling, which comprises a bowl-shaped or sleeve-shaped first coupling part that forms part of the upper ferrule part and a second coupling part that forms part of the lower ferrule part, wherein the second coupling part is insertable into the first coupling part by sliding in an axial direction of the upper ferrule part.

The above-mentioned first coupling part is provided with internal axial splines configured for engagement with corresponding external axial splines on the second coupling part in order to allow the second coupling part to slide axially in relation to the first coupling part during insertion of the second coupling part into the first coupling part, wherein said internal and external axial splines are configured to prevent the second coupling part from rotating and tilting in relation to the first coupling part when the internal axial splines and the external axial splines are in engagement with each other.

The above-mentioned second coupling part comprises a first snap-fit element and a second snap-fit element arranged on opposite sides of a centre axis of the lower ferrule part, wherein the first and second snap-fit elements fit into a respective one of two recesses formed in the first coupling part on opposite sides of a centre axis of the upper ferrule part, and wherein the first and second snap-fit elements, when received in the associated recesses, are configured to keep the second coupling part connected to the first coupling part, and thereby keep the lower ferrule part secured to the upper ferrule part. Each one of the first and second snap-fit elements is resiliently fixed to the lower ferrule part so as to allow the two snap-fit elements to be resiliently flexed inwards towards the centre axis of the lower ferrule part, for instance by pressing with the fingers, and allow each snap-fit element to spring back outwards and snap into engagement with the associated recess in the first coupling part when aligned with this recess. The snap-fit coupling between the upper and lower ferrule parts makes it easy for a person to replace a used lower ferrule part for another lower ferrule part, for instance in order to replace a worn-out lower ferrule part by a new ferrule part or in order to replace a lower ferrule part by a lower ferrule part of another type with other characteristics. Hereby, the ground-engaging lower ferrule part may be replaced in a simple and quick manner without having to remove the upper ferrule part from the crutch, cane, walking stick or ski stick. As mentioned above, the axial splines on the first and second coupling parts prevent the second coupling part from rotating and tilting in relation to the first coupling part when the external axial splines of the second coupling part are in engagement with the internal axial splines on the first coupling part. Thus, the second coupling part has to be moved in a straight axial movement in relation to the first coupling part in order to release the lower ferrule part from the upper ferrule part, which in its turn implies that the first and second snap-fit elements both have to be released from the associated recesses in first coupling part to make possible a removal of the lower ferrule part from the upper ferrule part. To make possible a simultaneous release of the first and second snap-fit elements from the associated recesses in the first coupling part, a person has to press simultaneously on the first and second snap-fit elements from opposite sides of the first coupling part, which prevents an accidental release of the lower ferrule part from the upper ferrule part in a situation when an individual snap-fit element is subjected to an accidental pressing force. Thus, the snap-fit coupling included in the ferrule of the present invention offers a reliable connection between the upper and lower ferrule parts, while still enabling a simple and quick release of the lower ferrule part from the upper ferrule part when so desired.

According to an embodiment of the invention, the ferrule comprises a locking member, which is moveably mounted to the upper ferrule part so as to be moveable between a locking position, in which the locking member prevents the first and second snap-fit elements from being flexed inwards towards the centre axis of the lower ferrule part when received in the associated recesses in the first coupling part, and an unlocking position, in which the locking member allows the first and second snap-fit elements to be resiliently flexed inwards towards the centre axis of the lower ferrule part when received in the associated recesses in the first coupling part. The locking member offers an improved security against accidental release of the lower ferrule part from the upper ferrule part.

According to another embodiment of the invention, the locking member comprises an annular base part rotatably mounted to the upper ferrule part, wherein the locking member is moveable between the locking position and the unlocking position by rotation of the base part in relation to the upper ferrule part about the centre axis of the upper ferrule part. Hereby, the locking member can be moved from the locking position to the unlocking position and from the unlocking position to the locking position in a simple manner. The base part of the locking member is preferably rotatably received in an external annular groove on the upper ferrule part, which facilitates the construction of the upper ferrule part and makes the base part of the locking member easily accessible when it is to be moved between the locking and unlocking positions.

To facilitate for a person to move the locking member between the locking and unlocking positions, the locking member preferably comprises at least one manoeuvring element, which is fixed to the base part of the locking member and projects in radial direction outwards from the base part in order to allow a person to rotate the base part in relation to the upper ferrule part by pushing or pulling on the manoeuvring element with a finger in the circumferential direction of the base part and thereby move the locking member between the locking position and the unlocking position. According to another embodiment of the invention, the locking member comprises a first locking element associated with the first snap-fit element and a second locking element associated with the second snap-fit element, wherein the first and second locking elements are fixed to the base part of the locking member so as to be rotatable in relation to the upper ferrule part together with the base part, wherein each locking element, when the locking member is in the locking position and the first and second snap-fit elements are received in the associated recesses in the first coupling part, is at least partially overlapped by the associated snap-fit element and thereby prevents the associated snap-fit element from being flexed inwards towards the centre axis of the lower ferrule part, and wherein each locking element, when the locking member is in the unlocking position and the first and second snap-fit elements are received in the associated recesses in the first coupling part, is offset from the associated snap-fit element and thereby allows the associated snap-fit element to be resiliently flexed inwards towards the centre axis of the lower ferrule part. Hereby, the locking of the snap-fit elements in the associated recesses can be achieved in a simple and reliable manner. The first and second locking elements preferably extend through a respective slot that is provided in the upper ferrule part and that extends along a section of the above- mentioned external annular groove on the upper ferrule part.

According to another embodiment of the invention, the first coupling part comprises a downwardly directed shoulder at its lower end, which is configured to abut against a corresponding upwardly directed shoulder on the lower ferrule part when the first and second snap-fit elements are received in the associated recesses in the first coupling part. When the lower ferrule part is pressed against the ground by the person using a crutch, cane, walking stick or ski stick equipped with the ferrule, forces are transmitted from the lower ferrule part to the upper ferrule part via said shoulders, which implies that no forces need to be transferred from the lower ferrule part to the upper ferrule part via the snap-fit elements. The service life of the snap-fit elements is thereby improved. Each snap-fit element is preferably located above said upwardly directed shoulder on the lower ferrule part and connected to this shoulder through one or more flexible legs.

The lower ferrule part preferably comprises a ground-engaging member of resiliently deformable high-friction materiel, for instance in the form of rubber or plastic material, wherein this ground-engaging member is fixed to the second coupling part. Hereby, the ferrule provides enhanced grip on slippery surfaces and also absorbs impacts. In order to offer a reliable grip on uneven surfaces, the ground-engaging member preferably has an external surface with convex shape. The ground-engaging member is with advantage bowl-shaped.

Another embodiment of the invention is characterized in:

- that the socket comprises a hollow and upwardly open cylindrical base and a nut, wherein the cylindrical base is fixed to the first coupling part and configured to receive a lower end portion of a crutch, cane, walking stick or ski stick and wherein the nut is configured for releasable engagement with the cylindrical base;

- that the cylindrical base is provided with an external thread configured for engagement with a corresponding internal thread provided in a through hole in the nut;

- that axially extending split sleeve arms are provided at an upper end of the cylindrical base and distributed about a centre axis of the cylindrical base, wherein the split sleeve arms are separated from each other in the circumferential direction of the cylindrical base by intermediate axial slits and together form a split sleeve that is configured to extend around the lower end portion of the crutch, cane, walking stick or ski stick received in the cylindrical base; and

- that a conical guide surface is provided in the through hole in the nut, wherein this conical guide surface is configured to press the split sleeve arms radially inwards towards the lower end portion of the crutch, cane, walking stick or ski stick received in the cylindrical base when the nut is screwed onto the cylindrical base to thereby clamp the socket to the lower end portion of the crutch, cane, walking stick or ski stick under the effect of the split sleeve arms and the nut.

Hereby, the upper ferrule part may be fixed to the lower end portion of a crutch, cane, walking stick or ski stick in a quick and reliable manner.

Further advantageous features of the ferrule according to the present invention will appear from the description following below and the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, a specific description of embodiments of the invention cited as examples follows below. In the drawings:

Fig 1 is a lateral view of a ferrule according to an embodiment of the present invention, as seen when mounted to a lower end portion of a crutch, cane, walking stick or ski stick,

Figs 2 and 3 are perspective views from different directions of the ferrule of Fig 1 ,

Fig 4 is an exploded perspective view of the ferrule of Fig 1 ,

Fig 5 is a perspective view of a part included in the ferrule of Fig 1 ,

Fig 6 is a planar view from below of an upper ferrule part included in the ferrule of Fig 1 ,

Fig 7a is a perspective view of the upper ferrule part of Fig 6, as seen with a locking member in a locking position, Fig 7b is a perspective view of the upper ferrule part of Fig 6, as seen with the locking member in an unlocking position,

Fig 8 is a planar view from above of the ferrule of Fig 1 ,

Fig 9 is a cut according to the line IX-IX in Fig 8,

Fig 10 is a cut according to the line X-X in Fig 1 ,

Fig 11 is a perspective view of a lower ferrule part included in the ferrule of Fig 1 ,

Fig 12 is a later view of the lower ferrule part of Fig 11 , and

Fig 13 is a later view of a lower ferrule part of an alternative type.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A ferrule 1 according to an embodiment of the present invention is illustrated in Figs 1-12. The ferrule 1 is detachably mountable to a lower end portion 2 of a crutch, cane, walking stick or ski stick 3, as schematically illustrated in Figs 1 and 9. The ferrule 1 comprises an upper ferrule part 1a with a socket 10 for detachable engagement with a lower end portion 2 of a crutch, cane, walking stick or ski stick and a ground-engaging lower ferrule part 1 b releasably mountable to the upper ferrule part 1 a.

In the illustrated embodiment, the socket 10 comprises a hollow and upwardly open cylindrical base 11 (see Figs 4 and 9) and a nut 12 configured for releasable engagement with the cylindrical base. The cylindrical base 11 is provided with an external thread 13 configured for engagement with a corresponding internal thread 14 provided in a through hole in the nut 12. A lower end portion 2 of a crutch, cane, walking stick or ski stick is insertable into the inner space of the cylindrical base 11 through an opening 15 at an upper end thereof. Split sleeve arms 16 are provided at an upper end of the cylindrical base 11 and distributed about the centre axis of the cylindrical base 11. Each split sleeve arm 16 extends in the axial direction of the cylindrical base 11 and the split sleeve arms 16 are separated from each other in the circumferential direction of the cylindrical base 11 by intermediate axial slits 17. The split sleeve arms 16 together form a split sleeve 18, which surrounds the opening 15 at the upper end of the cylindrical base 11 and which is configured to extend around the lower end portion 2 of the crutch, cane, walking stick or ski stick received in the cylindrical base 11. A conical guide surface 19 (see Fig 9) is provided in the through hole in the nut 12 above the internal thread 14 and configured to co-operate with the split sleeve arms 16. When the nut 12 is screwed onto the cylindrical base 11 , the conical guide surface 19 is configured to press the split sleeve arms 16 radially inwards towards the centre axis of the cylindrical base 11 and towards the lower end portion 2 of the crutch, cane, walking stick or ski stick received in the cylindrical base 11 to thereby clamp the socket 10 to the lower end portion 2 of the crutch, cane, walking stick or ski stick under the effect of the split sleeve arms 16 and the nut 12. If the gap between the split sleeve 18 and the external surface of the lower end portion 2 of the crutch, cane, walking stick or ski stick is too large to allow a sufficient clamping force between the split sleeve 18 and the lower end portion 2 of the crutch or walking stick, an adapter sleeve 4 with a suitable wall thickness may be inserted in the inner space of the cylindrical base 1 1 in order to fill up the gap between the split sleeve 18 and the lower end portion 2 of the crutch, cane, walking stick or ski stick. The adapter sleeve 4 is provided with a longitudinal slot 4a in order to allow the adapter sleeve 4 to be clamped against the lower end portion 2 of a crutch, cane, walking stick or ski stick received in the cylindrical base 11. Adapter sleeves 4 with different wall thicknesses may be provided in order to allow the ferrule 1 to be used with crutches, canes, walking sticks and ski sticks of various diameters. The socket 10 may of course also be designed in any other suitable manner, as long as it is capable of keeping the ferrule 1 secured to the lower end portion 2 of a crutch, cane, walking stick or ski stick in a reliable manner.

The lower ferrule part 1 b is releasably mountable to the upper ferrule part 1a through a snap-fit coupling 20, which comprises a bowl-shaped or sleeve-shaped first coupling part 20a that forms part of the upper ferrule part 1 a and a second coupling part 20b that forms part of the lower ferrule part 1 b. The above-mentioned cylindrical base 11 of the socket 10 is fixed to the first coupling part 20a. The second coupling part 20b is insertable into the first coupling part 20a by sliding in an axial direction of the upper ferrule part 1 a, i.e. in a direction in parallel with a centre axis 5 of the upper ferrule part 1 a. Thus, the second coupling part 20b is received inside the first coupling part 20a when the first and second coupling parts 20a, 20b are properly connected to each other.

In the illustrated embodiment, the cylindrical base 11 of the socket 10 and the first coupling part 20a are formed in one piece, for instance of plastic material. However, they may as an alternative be formed as two separate components, which are fixed to each other in any suitable manner.

The first coupling part 20a is provided with internal axial splines 21 configured for engagement with corresponding external axial splines 22 on the second coupling part 20b in order to control the movement of the second coupling part 20b in relation to the first coupling part 20a during insertion of the second coupling part 20b into the first coupling part 20a when the lower ferrule part 1 b is being mounted to the upper ferrule part 1 a and during a release of the second coupling part 20b from the first coupling part 20a when the lower ferrule part 1 b is being released from the upper ferrule part 1 a. The internal and external axial splines 21 , 22 co-operate in guiding the second coupling part 20b in a straight axial sliding movement in relation to the first coupling part 20a during insertion of the second coupling part 20b into the first coupling part 20a and during release of the second coupling part 20b from the first coupling part 20a. The splines 21 , 22 are configured to prevent the second coupling part 20b from rotating and tilting in relation to the first coupling part 20a when the internal axial splines 21 on the first coupling part 20a and the external axial splines 22 on the second coupling part 20b are in engagement with each other.

In the illustrated embodiment, the internal axial splines 21 on the first coupling part 20a are formed by radially extending projections 23 with intermediate gaps provided on an inner wall of the first coupling part, whereas the external axial splines 22 on the second coupling part 20b are formed by teeth 24, which are configured to fit into the gaps between the projections 23 on the first coupling part 20a and which are separated from each other by intermediate recesses 25 configured to receive the projections 23. The splines 21 , 22 may of course also be designed in any other suitable manner.

The second coupling part 20b comprises a first snap-fit element 26a and a second snap-fit element 26b arranged opposite to each other on opposite sides of a centre axis 6 of the lower ferrule part 1 b. The first and second snap-fit elements 26a, 26b fit into a respective one of two recesses 27a, 27b formed in the first coupling part 20a on opposite sides of the centre axis 5 of the upper ferrule part 1 a. When received in the associated recesses 27a, 27b, the first and second snap-fit elements 26a, 26b are configured to keep the second coupling part 20b connected to the first coupling part 20a and thereby keep the lower ferrule part 1 b secured to the upper ferrule part 1 a. Each snap-fit element 26a, 26b is resiliently fixed to the lower ferrule part 1 b so as to allow the two snap-fit elements to be resiliently flexed inwards towards the centre axis 6 of the lower ferrule part 1 b by a person pressing on the snap-fit elements 26a, 26b, for instance with the fingers, and allow each snap-fit element 26a, 26b to spring back outwards and snap into engagement with the associated recess 27a, 27b in the first coupling part 20a when the snap-fit element is in a position inside the first coupling part 20a in alignment with the associated recess. In the illustrated embodiment, each snap-fit element 26a, 26b has a convex or inclined outer guide surface 28 (see Figs 9 and 12), which is configured to co-operate with and slide against a corresponding conical or inclined inner guide surface 29 (see Fig 9) in the first coupling part 20a when the second coupling part 20b is moved axially into engagement with the first coupling part 20a. Under the effect of these guide surfaces 28, 29, the snap-fit elements 26a, 26b are resiliently pressed inwards towards the centre axis 6 of the lower ferrule part 1 b when the second coupling part 20b is pushed into the first coupling part 20a, to thereby allow the second coupling part 20b to slide axially into the first coupling part 20a, whereupon the snap-fit elements 26a, 26b snap radially outwards into engagement with the associated recesses 27a, 27b in the first coupling part 20a when they reach a position inside the first coupling part 20a in level with the recesses 27a, 27b.

When the snap-fit elements 26a, 26b are received in the associated recesses 27a, 27b, a downwardly directed shoulder 30 (see Figs 9 and 12) on each snap-fit element overlaps an upwardly directed edge 31 in the associated recess, which prevents the second coupling part 20b from sliding axially out of the first coupling part 20a. When the lower ferrule part 1 b is to be released from the upper ferrule part 1 a, a person has to press onto both snap-fit elements 26a, 26b simultaneously such that the snap-fit elements are flexed radially inwards to a position in which the downwardly directed shoulder 30 on each snap-fit element 26a, 26b goes free from the upwardly directed edge 31 in the associated recess 27a, 27b, whereupon the person may pull the second coupling part 20b in axial direction out of the first ferrule part 20a by pulling on the lower ferrule part 1 b to thereby release the lower ferrule part 1 b from the upper ferrule part 1 a. A new lower ferrule part 1 b of the same type or of another type with other characteristics may then be mounted to the upper ferrule part 1 a.

In the illustrated embodiment, the first coupling part 20a comprises a downwardly directed shoulder 32 (see Figs 7a and 9) at its lower end. As illustrated in Fig 9, this shoulder 32 is configured to abut against a corresponding upwardly directed shoulder 33 on the lower ferrule part 1 b when the snap-fit elements 26a, 26b are received in the associated recesses 27a, 27b in the first coupling part 1a. Thus, when the lower ferrule part 1 b is mounted to the upper ferrule part 1 a, the upper ferrule part 1 a bears against the lower ferrule part 1 b via these shoulders 32, 33 on the upper and lower ferrule parts. The first snap-fit element 26a is located above the upwardly directed shoulder 33 on the lower ferrule part 1 b and resiliently connected to this shoulder 33 through a flexible first leg 34a. In the corresponding manner, the second snap-fit element 26b is located above said shoulder 33 on the lower ferrule part 1 b and connected to this shoulder 33 through a flexible second leg 34b. However, the snap-fit elements 26a, 26b may as an alternative be resiliently fixed to the lower ferrule part 1 b in any other suitable manner.

In the illustrated embodiment, the lower ferrule part 1 b is provided with marking elements 42, which are mountable to the snap-fit elements 26a, 26b. In order to clearly distinguish between lower ferrule parts 1 b having different types of groundengaging members 40, lower ferrule parts 1 b with a first type of ground-engaging member 40 may be provided with marking elements 42 of a certain colour and lower ferrule parts 1 b’ with another type of ground-engaging member 40 may be provided with marking elements 42 of another colour. Such marking elements 42 are of course not compulsory.

The lower ferrule part 1 b preferably comprises a groundengaging member 40 of resiliently deformable high-friction materiel, for instance in the form of rubber or rubber-like plastic material, wherein this ground-engaging member 40 is fixed to the second coupling part 20b. The ground-engaging member 40 has an external surface with convex shape and is with advantage bowl-shaped. A lower ferrule part 1 b’ of an alternative type is illustrated in Fig 13, wherein this lower ferrule part 1 b’ has a ground-engaging member 40 provided with studs 41 in order to provide enhanced grip on ice. As to the rest, the lower ferrule part 1 b’ illustrated in Fig 13 has the same design as the lower ferrule part 1 b illustrated in Figs 1 -4, 9, 11 and 12.

The ferrule 1 preferably comprises a locking member 50, which is moveably mounted to the upper ferrule part 1a so as to be moveable between a locking position (see Figs 1-3, 5, 6, 7a, 8 and 9), in which the locking member 50 prevents the first and second snap-fit elements 26a, 26b from being flexed inwards towards the centre axis 5 of the lower ferrule part 1 b when received in the associated recesses 27a, 27b in the first coupling part 20a, and an unlocking position (see Fig 7b), in which the locking member 50 allows the first and second snap-fit elements 26a, 26b to be resiliently flexed inwards towards the centre axis 6 of the lower ferrule part 1 b when received in the associated recesses 27a, 27b in the first coupling part 20a.

In the illustrated embodiment, the locking member 50 comprises an annular base part 51 , which is rotatably mounted to the upper ferrule part 1 a by being rotatably received in an external annular groove 52 on the upper ferrule part. The external annular groove 52 is located between the cylindrical base 11 of the socket 10 and the first coupling part 20a. In this case, the locking member 50 is moveable between the locking position and the unlocking position by rotation of the base part 51 in relation to the upper ferrule part 1 a about the centre axis 5 of the upper ferrule part.

The locking member 50 comprises a first locking element 54a associated with the first snap-fit element 26a and a second locking element 54b associated with the second snap-fit element 26b. The first and second locking elements 54a, 54b are fixed to the base part 51 of the locking member 50 so as to be rotatable in relation to the upper ferrule part 1 a together with the base part 51. The locking member 50 is to be in the unlocking position when the second coupling part 20b is moved into engagement with the first coupling part 20a. In the unlocking position, the locking elements 54a, 54b are offset from the recesses 27a, 27b in the first coupling part 20a, as illustrated in Fig 7b, to thereby allow the snap-fit elements 26a, 26b to be received in these recesses 27a, 27b. Thus, in the unlocking position, the locking elements 54a, 54b are located at the side of said recesses 27a, 27b. When the snap-fit elements 26a, 26b have been properly received in the associated recesses 27a, 27b in the first coupling part 20a, the locking member 50 is moved to the locking position. In the locking position, each locking element 54a, 54b is located in a position behind the associated recess 27a, 27b in the first coupling part 20a, as illustrated in Figs 7a and 9, and overlapped by the associated snap-fit element 26a, 26 to thereby prevent the snap-fit element from being flexed inwards towards the centre axis 6 of the lower ferrule part 1 b. When the locking member 50 at a later moment is returned to the unlocking position, the locking elements 54a, 54b are moved away from the recesses 27a, 27b and the snap-fit elements 26a, 26b and thereby allow the snap-fit elements to be resiliently flexed inwards towards the centre axis 6 of the lower ferrule part 1 b, for instance by a person pressing onto the snap-fit elements with the fingers.

In the illustrated embodiment, the first and second locking elements 54a, 54b project in axial direction from a lower side of the base part 51 and extend through a respective slot 55a, 55b that is provided in the upper ferrule part 1a and that extends along a section of the external annular groove 52 on the upper ferrule part.

In the illustrated embodiment, the locking member 50 is provided with two manoeuvring elements 56a, 56b, which are fixed to the base part 51 of the locking member on opposite sides thereof and project in radial direction outwards from the base part 51. A person may rotate the base part 51 in relation to the upper ferrule part 1a by pushing or pulling on the manoeuvring elements 56a, 56b with the fingers in the circumferential direction of the base part 51 to thereby move the locking member 50 from the locking position to the unlocking position or from the unlocking position to the locking position.

In the illustrated embodiment, the locking position is marked with a first marking 57a on the upper ferrule part 1 a and the unlocking position is marked with a second marking 57b on the upper ferrule part 1 a. One 56a of the above-mentioned manoeuvring elements overlaps the first marking 57a when the locking member 50 is in the locking position and the second marking 57b when the locking member 50 is in the unlocking position, wherein the respective marking 57a, 57b can be seen through a through hole 58 in the manoeuvring element 56a.

One or more latch members 59 (see Fig 4) may be arranged in the external annular groove 52 on the upper ferrule part 1 a in order to latch the base part 51 of the locking member 50 when the locking member reaches the locking position, to thereby keep the locking member 50 in the locking position. The latch members 59 are configured to lose their grip with the base part 51 when the base part is subjected to a sufficient force in the direction towards the unlocking position.

The locking member 50 may of course also be designed in any other suitable manner.

The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a person with ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.